Yikes! Although honestly I CAN'T hear the ringing at 4kHz (again - I'm not sensitive to the area between 4-5kHz), but it does make me uncomfortable. I'm wondering if it's an artifact or something loose. Need to investigate. Note the FR above gives a hint of this.
One thing I noted is that the metal cover / cage fits on the cup very tightly on the right side. In other words, it will stay without the screws on (the metal binds with the wood - the cutout is a bit too small). Wondering if this tight coupling between the wood and metal cage is causing it to ring at a very specific frequency.
These waterfalls are at the standard -36/-35db floors.